Acetate has an active half life of 3 days. That doesn't mean that in 3 days its out of your system. it means in 3 days the active hormone is at half of what it was when you injected.
That being said, most people find that every other day pinning is sufficient to keep stable blood levels and less sides with tren ace. I have ran it M/W/F with no issues.
As far as a TIME of day to do it; whenever you want. dont over think this stuff. We're talking MINIMAL differences over pinning exactly 24 hours as opposed to 36 hours or w/e. Unless youre competing at a global level, just enjoy yourself. I find it easy to pin right before i go to bed because its right next to my night stand.